Eil Malk (also Mecherchar) is part of the Rock Islands, a group of small, rocky, mostly uninhabited islands in Palau's Southern Lagoon, between Koror and Peleliu.

There are about 70 other marine lakes located throughout the Rock Islands.

It is connected to the ocean through fissures and tunnels in the limestone of ancient Miocene reef.

papua salii[1] and possibly other species in the lake have evolved to be substantially different from their close relatives living in the nearby lagoons.

The oxygen concentration in the lake declines from about 6 mg/L at the surface to zero at 16 meters (at the chemocline).